RAILROAD ARRANGEMENTS.We are able to announce that arrangements have been made with the Pennsylvania Central, the Baltimore and Ohio, and the " Big Four," the three great through lines from Chicago to Washington, by which Physicians and their families can obtain transportation with return tickets at one and one third rates.Dr. Atkinson, the Secretary of the Association, informs us that the Western Passenger Association has refused to grant commutation upon the following roads: the Atchison, Topeka & Santa Fe, Burlington, Cedar Rapids & Northern, Burlington & Missouri, Chicago & Alton, Chicago & Northwestern, Chicago, Burlington & Northern, Chicago, Burlington & Quincy, Chicago, Milwaukee & St. Paul, Chicago, Rock Island & Pacific, Chicago, St. Paul, Minneapolis & Omaha, Chicago, St. Paul & Kansas, Hannibal & St. Joseph, Kansas City, St. Joseph & Council Bluff, Illinois Central, Iowa Central, Milwaukee & Northern, Milwaukee, Lake Shore & Western, Minneapolis